Transistors devices such as IGBTs (Insulated Gate Bipolar Transistors) or MOSFETs (Metal Oxide Semiconductor Field-Effect Transistors) are widely used for switching different types of electric loads. For example, transistor devices may be employed in power conversion applications, electric drive applications, or lighting applications, to name only a few.
An IGBT is a voltage controlled MOS transistor device that includes a collector region (often referred to as drain region) and an emitter region (often referred to as source region) that have complementary doping types (conductivity types). An IGBT further includes a gate electrode which is dielectrically insulated from a body region by a gate dielectric, is adjacent the body region, and extends adjacent the body region from the emitter region to a base region (drift region). The base region is arranged between the body region and the collector region. In the on-state of the IGBT the gate electrode generates a conducting channel in the body region between the emitter region and the drift region so that the emitter region can inject charge carriers of a first conductivity type into the drift region. At the same time, the collector region injects charge carriers of a second conductivity type into the drift region, with the charge carriers of the first and second conductivity types forming a charge carrier plasma in the drift region. This charge carrier plasma results in relatively low conduction losses of the IGBT.
Relevant operation parameters of an IGBT are the saturation voltage (often referred to as VCEsat) and the saturation current (often referred to as ICEsat). The saturation voltage is the voltage between the emitter and collector region of the IGBT at a typical current (rated current) in a normal operation mode of the IGBT. The saturation voltage characterizes the power losses that occur in a normal operation mode of the IGBT. The saturation current is the current that occurs at voltages much higher than the saturation voltage. The saturation current characterizes the behaviour of the IGBT in an overload scenario such as, for example, a short-circuit in the load. A high current in an overload scenario may damage associated circuitry.
It is desirable to design an IGBT with a low saturation voltage and a low saturation current, so as to have low losses in the normal operation mode and a low risk of damages in associated circuitry. However, conventional design measures that reduce the saturation voltage increase the saturation current. It is therefore desirable to adjust the saturation voltage of an IGBT widely independent of the saturation current.